I have Red Gate's SQL Prompt extension installed in SSMS. If I try to execute a delete or update without a where clause, it asks me to confirm that's what I want to do. It also clearly indicates in the editor that there's a problem. If I'm sure that's what I want to do and I want to avoid being warned I just add WHERE 1 = 1 to the end.

It's a nice feature that adds a little bit of comfort (though I'm still wary enough to hesitate before running SQL data modifications against production)